### What changes were proposed in this pull request?
This PR proposes to port the fix https://github.com/databricks/koalas/pull/2172.
```python
ks.DataFrame({'a': [1, 2, 3], 'b':["a", "b", "c"], 'c': [4, 5, 6]}).plot(kind='hist', x='a', y='c', bins=200)
```
**Before:**
```
pyspark.sql.utils.AnalysisException: cannot resolve 'least(min(a), min(b), min(c))' due to data type mismatch: The expressions should all have the same type, got LEAST(bigint, string, bigint).;
'Aggregate [unresolvedalias(least(min(a#1L), min(b#2), min(c#3L)), Some(org.apache.spark.sql.Column$$Lambda$1556/0x0000000800d9484042fb0cc1)), unresolvedalias(greatest(max(a#1L), max(b#2), max(c#3L)), Some(org.apache.spark.sql.Column$$Lambda$1556/0x0000000800d9484042fb0cc1))]
+- Project [a#1L, b#2, c#3L]
+- Project [__index_level_0__#0L, a#1L, b#2, c#3L, monotonically_increasing_id() AS __natural_order__#8L]
+- LogicalRDD [__index_level_0__#0L, a#1L, b#2, c#3L], false
```
**After:**
```python
Figure({
'data': [{'hovertemplate': 'variable=a<br>value=%{text}<br>count=%{y}',
'name': 'a',
...
```
### Why are the changes needed?
To match the behaviour with panadas' and allow users to set `x` and `y` in the DataFrame with non-numeric columns.
### Does this PR introduce _any_ user-facing change?
No to end users since the changes is not released yet. Yes to dev as described before.
### How was this patch tested?
Manually tested, added a test and tested in notebooks:
Closes#32884 from HyukjinKwon/fix-hist-plot.
Authored-by: Hyukjin Kwon <gurwls223@apache.org>
Signed-off-by: Hyukjin Kwon <gurwls223@apache.org>
### What changes were proposed in this pull request?
This PR proposes applying `black` to pandas API on Spark codes, for improving static analysis.
By executing the `./dev/reformat-python` in the spark home directory, all the code of the pandas API on Spark is fixed according to the static analysis rules.
### Why are the changes needed?
This can be reduces the cost of static analysis during development.
It has been used continuously for about a year in the Koalas project and its convenience has been proven.
### Does this PR introduce _any_ user-facing change?
No, it's dev-only.
### How was this patch tested?
Manually reformat the pandas API on Spark codes by running the `./dev/reformat-python`, and checked the `./dev/lint-python` is passed.
Closes#32779 from itholic/SPARK-35499.
Authored-by: itholic <haejoon.lee@databricks.com>
Signed-off-by: Liang-Chi Hsieh <viirya@gmail.com>
### What changes were proposed in this pull request?
There are still naming related to Koalas in test and function name. This PR addressed them to fit pandas-on-spark.
- kdf -> psdf
- kser -> psser
- kidx -> psidx
- kmidx -> psmidx
- to_koalas() -> to_pandas_on_spark()
### Why are the changes needed?
This is because the name Koalas is no longer used in PySpark.
### Does this PR introduce _any_ user-facing change?
`to_koalas()` function is renamed to `to_pandas_on_spark()`
### How was this patch tested?
Tested in local manually.
After changing the related naming, I checked them one by one.
Closes#32516 from itholic/SPARK-35364.
Authored-by: itholic <haejoon.lee@databricks.com>
Signed-off-by: Takuya UESHIN <ueshin@databricks.com>
### What changes were proposed in this pull request?
Consolidate PySpark testing utils by removing `python/pyspark/pandas/testing`, and then creating a file `pandasutils` under `python/pyspark/testing` for test utilities used in `pyspark/pandas`.
### Why are the changes needed?
`python/pyspark/pandas/testing` hold test utilites for pandas-on-spark, and `python/pyspark/testing` contain test utilities for pyspark. Consolidating them makes code cleaner and easier to maintain.
Updated import statements are as shown below:
- from pyspark.testing.sqlutils import SQLTestUtils
- from pyspark.testing.pandasutils import PandasOnSparkTestCase, TestUtils
(PandasOnSparkTestCase is the original ReusedSQLTestCase in `python/pyspark/pandas/testing/utils.py`)
Minor improvements include:
- Usage of missing library's requirement_message
- `except ImportError` rather than `except`
- import pyspark.pandas alias as `ps` rather than `pp`
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
Unit tests under python/pyspark/pandas/tests.
Closes#32177 from xinrong-databricks/port.merge_utils.
Authored-by: Xinrong Meng <xinrong.meng@databricks.com>
Signed-off-by: Takuya UESHIN <ueshin@databricks.com>
### What changes were proposed in this pull request?
Now that we merged the Koalas main code into the PySpark code base (#32036), we should port the Koalas plot unit tests to PySpark.
### Why are the changes needed?
Currently, the pandas-on-Spark modules are not tested fully. We should enable the plot unit tests.
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
Enable plot unit tests.
Closes#32151 from xinrong-databricks/port.plot_tests.
Authored-by: Xinrong Meng <xinrong.meng@databricks.com>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>
